Point-of-care testing and the search for effective biomarkers are important themes in biomedical research, e.g. Holland et al, Curr. Opin. Microbiol., 8: 504-509 (2005); Yager et al, Nature, 442: 412-418 (2006); Frank et al, Nature Reviews Drug Discovery, 2: 566-580 (2003); Sidransky, Nature Reviews Drug Discovery, 2: 210-218 (2002). Both endeavors are meant to improve the access and effectiveness of healthcare while reducing its costs. Point-of-care testing is analytical testing performed outside a central laboratory using a device that can be easily transported to the vicinity of the patient and that can be operated under field conditions without highly specialized personnel. In many acute care medical and bio-defense monitoring applications, rapid sample processing and test readouts are also required, e.g. Raja et al, Clinical Chemistry, 48: 1329-1337 (2002).
A biomarker is a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention, Atkinson et al, Clin. Pharmacol. Ther., 69: 89-95 (2001). Biomarkers vary widely in nature, ease of measurement, and correlation with physiological states of interest, e.g. Frank et al (cited above). Most point-of-care devices are designed to measure molecular biomarkers that have been extracted from a sample or specimen or that are found directly in a biological fluid, such as blood, Holland et al (cited above). There is significant interest in measuring cellular markers in point-of-care devices, but cellular markers typically require some form of imaging or a fluidics system in order to make cell-specific measurements, thereby adding a significant technical challenge over that posed by the measurement of molecular markers, e.g. Shapiro, Cytometry A, 60A: 115-124 (2004); Shapiro et al, Cytometry A, 69A: 620-630 (2006); Rodriquez et al, PLOS Medicine, 2(7): e182 (2005); Janossy et al, Clinical Cytometry, 50: 78-85 (2002); Toner et al, Annu. Rev. Biomed. Eng., 7: 77-103 (2005); and the like.
Point-of-care tests could be carried out on a wide range of sample types, including not only samples from individual organisms, such as medical, veterinary, or plant samples, but also samples from various environments, such as soils, water systems, air conditioner systems, surfaces in public places, such as transportation systems, and the like. Among medical samples, biological fluids, such as blood, saliva, tear duct fluid, urine, and the like, are especially amenable for use with point-of-care assays, as they are usually much more accessible than solid tissues. Among such biological fluids from which cellular or molecular markers can be obtained, blood is the sample of choice, whenever biologically relevant, because it systemic, it is easily accessible, and it contains a rich and dynamic suspension of cells and molecules whose composition reflects states of health and disease. In particular, there is great interest in being able to count certain subsets of non-red blood cells that are correlated with disease susceptibilities, disease progression, drug responsiveness, and the like, e.g. Guisset et al, Intensive Care Med., Epub (Nov. 8, 2006); Shaked et al, Curr. Cancer Drug Targets, 5: 551-559 (2005); Madjid et al, J. Am. Coll. Cardiol., 44: 1945-1956 (2004); Janossy et al (cited above); Rodriquez et al (cited above). Unfortunately, currently available analyzers for such markers suffer from one or more drawbacks that limit their widespread use, including complex preparation steps involving separation and/or cell lysis, involvement of specialized personnel, lack of portability, high cost, lack of sensitivity, and the like.
In view of the above, several medical and biotechnology fields would be significantly advanced with the availability of techniques, capable of point-of-care operation, which permitted facile and flexible measurements of cellular markers, particularly in biological fluids, such as blood.